xe2x80x83
100 etching device
102 processing chamber
104 processing container
106 lower electrode
108 matcher
110 biasing power supply
121 controller
114 upper electrode
114a gas outlet hole
116 insulating member
118 matcher
120 plasma generating power supply
122 gas supply pipe
124 evacuating pipe
200 substrate
202 insulating film
206 photoresist film
208 polymer (protective film)
210 contact hole
W wafer
The present invention relates to a plasma etching method.
There is a plasma etching device proposed in the prior art, having an upper electrode and a lower electrode provided facing opposite each other inside an air-tight processing chamber. In this device, after placing a workpiece such as a semiconductor wafer (hereafter referred to as a xe2x80x9cwaferxe2x80x9d) on the lower electrode, the processing gas is introduced into the processing chamber and also, vacuum drawing is implemented inside the processing chamber to maintain the atmosphere within at a specific pressure. Next, plasma generating power is applied to the upper electrode and biasing power sustaining a specific power level is applied to the lower electrode. As a result, the processing gas inside the processing chamber becomes dissociated to generate plasma and radicals, and an insulating film such as an SiO2 (silicon oxide) film formed on the wafer becomes etched through ion-assist etching by the radicals and the ions in the plasma drawn into the wafer by the biasing power, thereby forming contact holes at the insulating film.
However, when forming contact holes in conformance to the 0.15 xcexcm design rule, a higher aspect ratio must be achieved and thus, the etching rate at the insulating film is lowered. In addition, the photoresist film formed at the surface of the insulating film is constantly sputtered with the ions. During this process, the comers formed between the upper surface of the photoresist film and the pattern formation surface tend to be sputtered to a great degree. Consequently, the pattern width of the photoresist film 206 increases as shown in FIG. 2(d), presenting a problem in that a desired contact hole 210 cannot be formed. Accordingly, it is essential to achieve a technology that increases the ratio of the etching rate (or the etching quantity) at the insulating film 202 relative to the etching rate (or the etching quantity) at the photoresist film 206 (hereafter referred to as the xe2x80x9cselectivityxe2x80x9d).
An object of the present invention, which has been completed by addressing the problem of the prior art discussed above, is to provide a new and improved plasma etching method that improves the etching selectivity and enables an ultra-fine etching process to be implemented on a workpiece.
In order to achieve the object described above, in a first aspect of the present invention, a plasma etching method for implementing a specific etching process on a workpiece placed on an electrode provided within a processing chamber by introducing a processing gas into the processing chamber, generating plasma inside the processing chamber with a plasma source and applying biasing power to the electrode, which is characterized in that an etching step in which the workpiece is etched over a specific length of etching time by applying the biasing power to the electrode and a film formation step in which a protective film is formed as an etching mask at a surface of the workpiece over a specific length of film formation time while the biasing power is cut off are sequentially repeated, with the lengths of the individual etching times and the individual film formation times adjusted as the etching process progresses, is provided.
In a second aspect of the present invention, a plasma etching method for implementing a specific etching process on a workpiece placed on an electrode provided within a processing chamber by introducing a processing gas into the processing chamber, generating plasma inside the processing chamber with a plasma source and applying biasing power to the electrode, which is characterized in that an etching step in which a workpiece is etched over a specific length of etching time by applying the biasing power to the electrode and a film formation step in which a protective film is formed as an etching mask at a surface of the workpiece over a specific length of film formation time while the biasing power is cut off are sequentially repeated, with the process starting with the film formation step and ending with the etching step is provided.
Adopting such an etching method, in which the etching process is implemented by repetitively performing the etching step and the film formation step, makes it possible to etch the workpiece while protecting the etching mask such as a photoresist film with the protective film. As a result, since the photoresist film is not readily etched and higher selectivity is achieved, the pattern at the photoresist film is prevented from spreading. In addition, since the protective film is formed at the mask pattern sidewalls during the film formation step, desired contact holes can be formed at the workpiece.
By adjusting the lengths of the individual etching times and the individual film formation times as the etching process progresses, a desired etching process can be implemented even if the states of the workpiece and the photoresist film change during the process.
Furthermore, the lengths of the individual film formation times may be extended as the etching process progresses. As the process progresses, the aspect ratio of the contact holes increases, which makes it difficult to form a protective film at the bottom surfaces of the contact holes. Thus, by extending the lengths of the individual film formation times, it is possible to ensure that the photoresist film is protected with a higher degree of reliability while implementing a specific etching process.
In addition, by setting the lengths of the individual film formation times at one second or longer, the protective film can be formed at the photoresist film with a high degree of reliability during the film formation steps.
By implementing an etching step at the end of the etching process, the protective film formed at the bottom surfaces of the contact holes and the photoresist film can be removed, thereby eliminating the need to implement a step for removing the protective film to allow the post-process to be completed promptly.
Furthermore, by implementing a film formation step at the beginning of the etching process, the photoresist film becomes protected by the protective film prior to the etching step, thereby enabling a desired process to be implemented on the workpiece.
Moreover, by constituting the etching target with a silicon oxide film and using a gas containing fluorocarbon gas as the processing gas, a protective film can be formed at the photoresist with a high degree of reliability and desired contact holes can be formed at the CSiO2 film.